The present invention relates to a method of making an ultra soft, multi-ply tissue having a high basis weight using wet press technology. More particularly, the invention relates to an ultra soft bathroom tissue produced using wet press technology.
In the area of bathroom tissue, softness, absorbency and strength are key attributes considered by consumers. It is highly desirable that the tissue product have a consumer perceived feel of softness. This softness plays a key role in consumer preference. Softness relates both to the product bulk and surface characteristics. In addition to softness, the consumer desires a product that is both strong and absorbent to minimize the amount of the product which must be used to do an effective job.
The method of the present invention uses wet press technology to prepare a strong, ultra soft tissue having a high basis weight. The tissue produced by the method of the present invention exhibits good strength and absorbency while remaining extremely soft. Properties such as those exhibited by the tissue produced by the present invention have previously only been seen on products produced by costly Through-Air-Drying (TAD) technology. The tissue according to the present invention has properties like those of the TAD produced tissue but can be formed using more efficient, less expensive wet press technology.
In a conventional wet press process and apparatus (10), as exemplified in FIG. 1, a furnish is fed from silo (50) through conduits (40, 41) to headbox chambers (20, 20xe2x80x2). A web (W) is formed on a conventional wire former (12), supported by rolls (18, 19), from a liquid slurry of pulp, water and other chemicals. Materials removed from the web of fabric by Uhle box (29) through the forming fabric when pressed against forming roll (15) are returned to silo (50), from saveall (22) through conduit (24). The web is then transferred to a moving felt or fabric (14), supported by roll (11) for drying and pressing. Materials removed from the web during drying and pressing are collected in saveall (44) and fed to white water conduit (45). The web is then pressed by suction press roll (16) against the surface of a rotating Yankee dryer cylinder (26) which is heated to cause the paper to substantially dry on the cylinder surface. The moisture within the web as it is laid on the Yankee surface causes the web to transfer to the surface. Liquid adhesive may be applied to the surface of the dryer to provide substantial adherence of the web to the creping surface. The web is then creped from the surface with a creping blade (27). The creped web is then usually passed between calender rollers and rolled up on roll (28) prior to further converting operations, for example, embossing. The action of the creping blade on the paper is known to cause a portion of the interfiber bonds within the paper to be broken up by the mechanical smashing action of the blade against the web as it is being driven into the blade. However, fairly strong interfiber bonds are formed between the wood pulp fibers during the drying of the moisture from the web. The strength of these bonds in prior art tissues is such that even after creping, the web retains a perceived feeling of hardness, a fairly high density, and low-bulk and water absorbency.
To reduce the strength of the interfiber bonds that inevitably result when wet pressing and drying a web from a slurry, various processes have been utilized. One such process is the passing of heated air through the wet fibrous web after it is formed on a wire and transferred to a permeable carrierxe2x80x94a so-called through-air-dried (TAD) processxe2x80x94so that the web is not compacted prior to being dried. The lack of compaction, such as would occur when the web is pressed while on a felt or fabric and against the drying cylinder when it is transferred thereto, reduces the opportunity for interfiber bonding to occur, and allows the finished product to have greater bulk than can be achieved in a wet press process. Because of the consumer perceived softness of these products, and their greater ability to absorb liquids than webs formed in wet press processes, the products formed by the newer processes enjoy an advantage in consumer acceptance.
Felted wet press processes are significantly more energy efficient than processes such as through-air-drying since they do not require heating and moving large quantities of air as required by the TAD process. In wet press operations, excess moisture is mechanically pressed from the web and the final drying of the web is obtained chiefly on the heated Yankee drying cylinder which is maintained at the proper drying temperature.
The present invention provides a method for making a tissue product that achieves high bulk, absorbency and softness above existing conventional wet press technology tissue, approaching or achieving the levels found using through-air-drying while using the cheaper more efficient wet press process.
Further advantages of the invention will be set forth in part in the description which follows and in part will be apparent from the description. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is disclosed:
A method of making an ultra-soft high basis weight multi-ply tissue comprising:
(a) providing a fibrous pulp including 35 to 90% of a first fiber, wherein the first fiber has an average fiber length of 2.0 mm or less and a coarseness of 12 mg/100 meters or less;
and including 10 to 65% of a second fiber having an average fiber length greater than 2.0 mm and a coarseness of less than 35 mg/100 meters
wherein the pulp further includes up to about 5 lb/ton of a strength adjusting agent;
(b) forming a first nascent web from the pulp, wherein the first web has a basis weight of at least about 11 lbs/3000 sq. ft. ream;
(c) including in the first web at least about 1.0 lbs/ton of a cationic nitrogenous softener;
(d) dewatering the first web through wet pressing;
(e) adhering the first web to a Yankee dryer;
(f) creping the first web from the Yankee dryer, wherein the adhesion between the first web and the Yankee dryer is controlled to achieve a reel crepe of at least about 20%;
(g) forming a second nascent web as recited in steps (a)-(f) above;
(h) combining the first web with the second web to form a multi-ply web;
(i) wherein either the first and second webs are calendered individually prior to combination into a multi-ply web or the multi-ply web is calendered; and
wherein steps (a)-(f), (g) and (i) are controlled to result in a multi-ply tissue product having an MD tensile strength of about 27 to about 38 g/3xe2x80x3 width per lb. of basis weight, a CD tensile strength of about 10 to about 23 g/3xe2x80x3 width per lb. of basis weight, a caliper of at least about 3 mils/lb. basis weight, a GM MMD friction of less than about 0.190, and a tensile stiffness of less than about 0.72 g/% strain per lb. of basis weight.
There is further disclosed an ultra soft, high absorbency product produced by the above-described method.
There is still further disclosed a method of making an ultra-soft high basis weight multi-ply tissue comprising:
(a) providing a fibrous pulp including 35 to 90% of a first fiber, wherein the first fiber has an average fiber length of 2.0 mm or less and a coarseness of 12 mg/100 meters or less;
and including 10 to 65% of a second fiber having an average fiber length greater than 2.0 mm and a coarseness of less than 35 mg/100 meters
wherein the pulp further includes up to about 5 lb/ton of a strength adjusting agent;
(b) forming a first nascent web from the pulp, wherein the first web has a basis weight of at least about 11 lbs/3000 sq. ft. ream;
(c) dewatering the first web through wet pressing;
(d) adhering the first web to a Yankee dryer;
(e) creping the first web from the Yankee dryer, wherein the adhesion between the first web and the Yankee dryer is controlled to achieve a reel crepe of at least about 20%;
(f) forming a second nascent web as recited in steps (a)-(e) above;
(g) combining the first web with the second web to form a multi-ply web;
(h) wherein either the first and second webs are calendered individually prior to combination into a multi-ply web or the multi-ply web is calendered;
(i) wherein the multi-ply web is sprayed with a softener to result in a web containing at least about 1.0 lb/ton of softener; and
wherein steps (a)-(f), (h) and (i) are controlled to result in a multi-ply tissue product having an MD tensile strength of about 27 to about 38 g/3xe2x80x3 width per lb. of basis weight, a CD tensile strength of about 10 to about 23 g/3xe2x80x3 width per lb. of basis weight, a caliper of at least about 3 mils/lb. basis weight, a GM MMD friction of less than about 0.190, and a tensile stiffness of less than about 0.72 g/% strain per lb. of basis weight.